DUBLIN, Jan 30 (Reuters) - Ireland's Prime Minister Enda Kenny apologised on Thursday to a woman who suffered sexual abuse by a teacher while at a Catholic-run school in 1973, after a European court ruled the state had failed to protect her.

The European Court of Human Rights this week ordered Ireland to pay compensation to Louise O'Keeffe, ruling the state had not met its obligation to protect children, even though it must have been aware by then of sexual abuse of children by adults.

"I would like to say to Louise O'Keeffe that I apologise for what happened to her...and for the whole horrendous experience that she had to go through," Kenny told a news conference.

The authority of the Catholic church in Ireland and its reputation worldwide have been rocked by investigations into clerical sex abuse and state-abetted cover-ups at Catholic-run schools and institutions, labelled places of fear and neglect in a 2009 official report.

The assaults by a lay teacher against O'Keeffe when she was nine took place at a public school, albeit owned by the Catholic Diocese of Cork and Ross and managed by a priest.

Ireland has started to address abuse in church-run institutions and has apologised for several previous cases.

"Sadly it's one that's indicative of the long litany of cases in Ireland," Kenny said. "That's why in the past we have had to deal with some exceptionally sensitive cases that scar our memory." (Reporting by Sam Cage; Editing by Raissa Kasolowsky)